I Have Hair Lost At The Crown Of My Head.

I have hair lost at the crown of my head. Before I started losing my hair I went on a metabolic diet. I have diabetes and high blood pressure. I use to take gabapentin also. The dr. Took me off when I was on that diet. What could have happen to make me lose hair. I want to try his diet again. Hair haven't grown back yet. Will I ever be able to grown it again. Now it had been 2 years.